This invention relates generally to impact testing apparatus, and in particular to launch apparatus for consistently and precisely projecting ice balls for testing structural component materials in connection with product grading and performance studies, new product design evaluation, as well as structural failure and property damage analysis, for example in simulating hail damage to roof shingles, skylights, vehicle windshields, automobile roof panels, aircraft fuselage panels, aircraft wing panels and the like.
Hail is showery precipitation in the form of irregular pellets or balls of ice typically more than about ⅓ inch in diameter. Hail usually free-falls from a cumulonimbus cloud. Sometimes severe thunderstorms or tornadic storms bring about hail storms. Hail is a major cause of damage to structures such as roof shingles, skylights, vehicle windshields, automobile roof panels and aircraft fuselage panels, leading to many insurance claims. Although conventional impact test procedures and equipment have been devised for assessing the structural integrity and strength of various structural component materials, such equipment for simulating the effect of hail impact has not previously been available. The ability of a material to resist hail damage is of considerable interest to structural engineers and the insurance underwriting industry.
There is, therefore, a need for impact test equipment that can repeatedly and precisely project ice balls at predetermined, consistent impact energy levels in connection with a testing protocol that simulates the impact of hail on various materials to determine relative ability or strength of a building material or structural component to withstand hail damage. Such equipment is needed, for example, for testing structural materials in connection with product quality grading and performance studies, new product design and development evaluations, as well as structural failure and property damage analysis, for example in simulating hail damage to roof shingles.
In accordance with one aspect of the present invention, an ice ball launcher is provided. The ice ball launcher includes a base member, a rail, a sled, an ice ball holder, a trigger latch assembly, one or more elastic bands and an aiming device. The rail is adjustably attached to the base member, and the rail has a channel portion thereon. The sled is slidably coupled with the channel portion on the rail. The ice ball holder is removably attached to the sled. The ice ball holder has an interior configuration adapted to bias against and releasably retain an ice ball therein. One or more elastic bands extend to and engage with the sled. The launcher is configured such that the elastic band is in a stretched condition under predetermined tension pulling on the sled when the sled is in a cocked position and the trigger latch assembly is engaged. The aiming device is attached to the base member in alignment with the rail, assuring precision placement of the ice ball impact onto a target area of interest. A protective shield is attached to the base member and extends generally perpendicular to the rail.
In accordance with another aspect of the present invention, an ice ball launcher is provided in which the ice ball holder includes a cup member that has a groove formed there through that extends partially about the cup member in a circumferential direction. A reed member is attached to an interior surface of the cup member at one end of the reed member such that the reed member extends across at least a portion of the groove. The elastic band is located about the cup member within the groove. The elastic band has a relaxed diameter less than the outer diameter of the cup member where the groove is located such that the elastic band extends into the cup member and biases against the reed member.
The aiming device is attached to the base member in alignment with the longitudinal axis of the rail. In the preferred embodiment the aiming device includes a low power laser that emits a visible laser beam that projects a small red dot onto the target surface. Column posts are mounted on either side of the rail for engaging the band and arresting forward movement of the sled at a predetermined travel limit stop point. The column posts serve as stops for engaging a central portion of the elastic band to limit a range of forward motion of the sled. The ice ball is only lightly retained within the cup and the retaining force applied by the holder is easily overcome by the forward momentum and kinetic energy of the ice ball as movement of the sled is arrested at the stop point.
According to one aspect of the invention, a velocity measuring apparatus is provided to measure the velocity of an ice ball as it is projected from the ice ball launcher. The ice ball velocity measurement is taken in order to calculate the impact energy and thus assure that the impact energy on target is within a desired tolerance range for uniform testing purposes. The velocity measuring apparatus includes a first light source, a first light sensor, a second light source, a second light sensor, and an electrical timing circuit. The first light sensor is positioned to receive light from the first light source. The second light sensor is positioned to receive light from the second light source. The second light sensor is located at a fixed distance away from the first light sensor. The electrical circuit is adapted to: detect a change in output from the first light sensor; detect a change in output from the second light sensor; measure a time between the detected change in output from the first light sensor and the detected change in output from the second light sensor, and calculate the velocity of an ice ball first passing between the first light source and the first light sensor and then passing between the second light source and the second light sensor.
In accordance with yet another aspect of the present invention, a method of simulating hail stone impact is provided for testing structural component samples, for example roof shingles. The method includes the following steps, the order of which may vary. First, an ice ball of a predetermined size is molded. Next, an installation mock-up(e.g., a roof section) having component samples (e.g., roofing shingles) installed thereon is set up. Then, the ice ball launcher is set up at a predetermined distance from the installation mock-up and aimed generally at a predetermined projection angle toward the mockup. The sled is then retracted to the latched position in which the elastic band is stretched to a predetermined tension level, and an ice ball is loaded into the cup. The launcher is then aimed precisely with the aid of a laser beam onto a desired target area. The trigger is manually actuated, thus releasing the sled, and the ice ball is projected from the cup at a predetermined velocity within a predetermined velocity range onto a specific location on the component sample within an aiming point area tolerance.
The method may further include the steps of measuring the velocity of the ice ball as it projects from the ice ball launcher to the installation mockup, verifying that the ice ball velocity is within the predetermined velocity tolerance range, calculating an impact energy of the ice ball impacting the component sample material, and determining whether the calculated impact energy is within a predetermined impact energy tolerance range.